This application claims the priority of German patent 198 32 142.2, filed Jul. 17, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method for manufacturing a hollow body from two plates, which are inserted resting against one other into an internal high pressure forming tool, and, after the forming tool is closed, by introducing a fluid under high pressure between the plates by way of an expansion lance inserted between them, are pushed apart until they abut the hollow in the forming tool that matches the shape of the hollow body. The invention also relates to a device for manufacturing a hollow body from two plates placed against one another, with an internal high pressure forming tool and an expansion lance that can be introduced between the plates and has a feed bore for introducing a fluid under high pressure between the plates, with the forming tool having a mold chamber formed by its hollow parts which corresponds to the shape of the hollow body to be formed.
A method and a device of the type generally described above are known from German patent document DE 44 16 147 A1 (corresponding to U.S. Pat. No. 5,711,059). In this document, two plates are placed against one another and welded together edgewise in their lengthwise direction, and this combination of plates is then placed in an internal high pressure forming tool, which has a mold chamber formed by the hollows of the dies of the forming tool. The forming tool is then closed, whereupon the plates are clamped between the dies with a high force. To introduce the pressure fluid between the plates, a splitting chisel is introduced between the plates and the hole left by the chisel is used to fill the plates with a pressure fluid under high pressure. The plates subjected to this pressure then expand in the area of the mold chamber. However, it is disadvantageous that when the objects to be shaped are large, the insertion of the plate edges is restricted by the closing force of the forming tool acting on the plates in such fashion that the stretch limit of the material is soon reached and tears develop in the resultant hollow profile, causing the forming process to be interrupted.
It is known from European patent document EP 0 589 370 A1 that when the plates are being manufactured, shapes can be produced in them so that a channel results when they are placed against one another, said channel permitting easier penetration of high-pressure fluid between the plates. After the two plates are joined, the plate combination is inserted into an internal high-pressure forming tool and the tool is closed. The closing force of the forming tool determines the clamping force for the plates located in between. At the filling opening from which the channel takes its departure, a conical mandrel or a lance provided with a feed bore is applied, sealed by an annular bead. Then the fluid, under high pressure, flows through the feed bore between the plates and spreads them. As a result, when a hollow profile is produced from the two plates, the problems outlined above regarding the reliability of the process and the method occur.
The goal of the invention is to improve a method and a device for manufacturing a hollow body from two plates such that reliable manufacture of the hollow body is achieved.
This and other goals have been achieved according to the present invention by providing a method for manufacturing a hollow body from two plates, comprising the acts of: placing two plates resting against each other into an internal high pressure forming tool having an interior surface defining a mold chamber; inserting an expansion lance between the plates, the plates being pinched between the forming tool and a circumferential contour of the expansion lance at an opening between the plates; introducing a fluid under high pressure between the plates via said expansion lance, said fluid pushing the plates apart until the plates abut the interior surface of the forming tool; and pushing material of said plates toward the mold chamber via a stop located on said expansion lance which abuts edges of said plates, during said introducing act.
This and other goals have been achieved according to the present invention by providing a device for manufacturing a hollow body from two plates, comprising: an internal high pressure forming tool having an interior surface defining a mold chamber corresponding to a shape of the hollow body, said forming tool receiving two plates resting against each other; an expansion lance insertable between the plates via an axial drive, the expansion lance and the axial drive forming a pushing plunger, the expansion lance having a pinching section along a circumferential contour, the plates to be pinched between said pinching section and the forming tool, said expansion lance including a feed bore communicable with a high pressure fluid source, said expansion lance defining an axial stop to abut axial edges of the plates, said axial stop having a radial periphery which is smaller than that of the mold chamber.
According to the invention, plate material is actively fed from the edge area to the mold chamber so that the tensile stresses that result from the clamping of the plates between the dies and the expansion lance are reduced, and the threshold of stretching is raised. The resultant thinning of the material is counteracted so that tears do not result in the material that lead to the bursting of the hollow body being formed. Consequently, hollow bodies can be produced even with high degrees of forming ( greater than 30 percent), in other words voluminous hollow bodies, without there being the danger of a breakdown in production caused by damage. As a result of the clamping of the plates by pinching, a higher degree of sealing ability is achieved which is extremely beneficial for the reliability of the process in working the manufacturing method.